swap: go back to using swapon for Linux systems

There are several reasons for going back to this:

- fstabinfo doesn't work with labels in fstab
- when a device is passed to swapon individually, the swap priority from
  fstab is not honored.
- We also add the -e option to only activate available swap devices.

reported-by: Duncan <1i5t5.duncan@cox.net>
X-Gentoo-Bug: 405021
X-Gentoo-Bug-URL: https://bugs.gentoo.org/show_bug.cgi?id=405021

init.d/swap.in

@@ -12,15 +12,7 @@ start()
 {
 	ebegin "Activating swap devices"
 	case "$RC_UNAME" in
-		Linux)
-			local dev
-			for dev in $(fstabinfo -b -t swap); do
-				case "$dev" in
-					/dev/loop*) ;;
-					*) swapon $dev >/dev/null;;
-				esac
-			done
-			;;
+		Linux)		swapon -a -e >/dev/null;;
 		NetBSD|OpenBSD) swapctl -A -t noblk >/dev/null;;
 		*)		swapon -a >/dev/null;;
 	esac